# characters that represent the UTF-8 bytes of each original character.

utf8::encode($string);# "\x{100}" becomes "\xc4\x80"

utf8::decode($string);# "\xc4\x80" becomes "\x{100}"

$flag = utf8::is_utf8(STRING);# since Perl 5.8.1

$flag = utf8::valid(STRING);

DESCRIPTION

The useutf8
pragma tells the Perl parser to allow UTF-8 in the
program text in the current lexical scope (allow UTF-EBCDIC on EBCDIC based
platforms). The noutf8
pragma tells Perl to switch back to treating
the source text as literal bytes in the current lexical scope.

Do not use this pragma for anything else than telling Perl that your
script is written in UTF-8. The utility functions described below are
directly usable without useutf8;
.

Because it is not possible to reliably tell UTF-8 from native 8 bit
encodings, you need either a Byte Order Mark at the beginning of your
source code, or useutf8;
, to instruct perl.

When UTF-8 becomes the standard source format, this pragma will
effectively become a no-op. For convenience in what follows the term
UTF-X is used to refer to UTF-8 on ASCII and ISO Latin based
platforms and UTF-EBCDIC on EBCDIC based platforms.

See also the effects of the -C
switch and its cousin, the
$ENV{PERL_UNICODE}
, in perlrun.

Enabling the utf8
pragma has the following effect:

Bytes in the source text that have their high-bit set will be treated
as being part of a literal UTF-X sequence. This includes most
literals such as identifier names, string constants, and constant
regular expression patterns.

On EBCDIC platforms characters in the Latin 1 character set are
treated as being part of a literal UTF-EBCDIC character.

Note that if you have bytes with the eighth bit on in your script
(for example embedded Latin-1 in your string literals), useutf8
will be unhappy since the bytes are most probably not well-formed
UTF-X. If you want to have such bytes under useutf8
, you can disable
this pragma until the end the block (or file, if at top level) by
noutf8;
.

Utility functions

The following functions are defined in the utf8::
package by the
Perl core. You do not need to say useutf8
to use these and in fact
you should not say that unless you really want to have UTF-8 source code.

$num_octets = utf8::upgrade($string)

Converts in-place the internal representation of the string from an octet
sequence in the native encoding (Latin-1 or EBCDIC) to UTF-X. The
logical character sequence itself is unchanged. If $string is already
stored as UTF-X, then this is a no-op. Returns the
number of octets necessary to represent the string as UTF-X. Can be
used to make sure that the UTF-8 flag is on, so that \w
or lc()
work as Unicode on strings containing characters in the range 0x80-0xFF
(on ASCII and derivatives).

Note that this function does not handle arbitrary encodings.
Therefore Encode is recommended for the general purposes; see also
Encode.

$success = utf8::downgrade($string[, FAIL_OK])

Converts in-place the the internal representation of the string from
UTF-X to the equivalent octet sequence in the native encoding (Latin-1
or EBCDIC). The logical character sequence itself is unchanged. If
$string is already stored as native 8 bit, then this is a no-op. Can
be used to
make sure that the UTF-8 flag is off, e.g. when you want to make sure
that the substr() or length() function works with the usually faster
byte algorithm.

Fails if the original UTF-X sequence cannot be represented in the
native 8 bit encoding. On failure dies or, if the value of FAIL_OK
is
true, returns false.

Returns true on success.

Note that this function does not handle arbitrary encodings.
Therefore Encode is recommended for the general purposes; see also
Encode.

utf8::encode($string)

Converts in-place the character sequence to the corresponding octet
sequence in UTF-X. That is, every (possibly wide) character gets
replaced with a sequence of one or more characters that represent the
individual UTF-X bytes of the character. The UTF8 flag is turned off.
Returns nothing.

utf8::encode($a);# $a contains two characters, with ords 0xc4 and 0x80

Note that this function does not handle arbitrary encodings.
Therefore Encode is recommended for the general purposes; see also
Encode.

$success = utf8::decode($string)

Attempts to convert in-place the octet sequence in UTF-X to the
corresponding character sequence. That is, it replaces each sequence of
characters in the string whose ords represent a valid UTF-X byte
sequence, with the corresponding single character. The UTF-8 flag is
turned on only if the source string contains multiple-byte UTF-X
characters. If $string is invalid as UTF-X, returns false;
otherwise returns true.

Note that this function does not handle arbitrary encodings.
Therefore Encode is recommended for the general purposes; see also
Encode.

$flag = utf8::is_utf8(STRING)

(Since Perl 5.8.1) Test whether STRING is in UTF-8 internally.
Functionally the same as Encode::is_utf8().

$flag = utf8::valid(STRING)

[INTERNAL] Test whether STRING is in a consistent state regarding
UTF-8. Will return true is well-formed UTF-8 and has the UTF-8 flag
on or if string is held as bytes (both these states are 'consistent').
Main reason for this routine is to allow Perl's testsuite to check
that operations have left strings in a consistent state. You most
probably want to use utf8::is_utf8() instead.

utf8::encode
is like utf8::upgrade
, but the UTF8 flag is
cleared. See perlunicode for more on the UTF8 flag and the C API
functions sv_utf8_upgrade
, sv_utf8_downgrade
, sv_utf8_encode
,
and sv_utf8_decode
, which are wrapped by the Perl functions
utf8::upgrade
, utf8::downgrade
, utf8::encode
and
utf8::decode
. Also, the functions utf8::is_utf8, utf8::valid,
utf8::encode, utf8::decode, utf8::upgrade, and utf8::downgrade are
actually internal, and thus always available, without a requireutf8
statement.

BUGS

One can have Unicode in identifier names, but not in package/class or
subroutine names. While some limited functionality towards this does
exist as of Perl 5.8.0, that is more accidental than designed; use of
Unicode for the said purposes is unsupported.

One reason of this unfinishedness is its (currently) inherent
unportability: since both package names and subroutine names may need
to be mapped to file and directory names, the Unicode capability of
the filesystem becomes important-- and there unfortunately aren't
portable answers.